tailieunhanh - SOIL ECOLOGY IN SUSTAINABLE AGRICULTURAL SYSTEMS - CHAPTER 2

Tương tác giữa sinh vật đất, đất vật chất hữu cơ, và cơ cấu đất Cơ chế bảo vệ vật lý là những yếu tố quyết định quan trọng của sự ổn định của vật chất hữu cơ trong đất. Điều này một phần dựa trên quan sát rằng tỷ lệ doanh thu của các hợp chất dễ phân huỷ cao hơn nhiều trong nền văn hóa của vi sinh vật lỏng hơn so với trong đất (Van Veen và Paul, 1981), và trên các nghiên cứu kính hiển vi điện tử đã chứng minh các trang web tích lũy. | CHAPTER 2 Interactions Between Soil Biota Soil Organic Matter and Soil Structure J. Hassink F. J. Matus C. Chenu and J. W. Dalenberg INTRODUCTION Physical protection mechanisms are important determinants of the stability of organic matter in soils. This is partly based on the observation that the turnover rates of easily decomposable compounds are much higher in liquid microbial cultures than in soils Van Veen and Paul 1981 and on electron microscopy studies that have demonstrated sites of accumulation of organic residues of clearly cellular origin Foster 1988 . The phenomenon that drying of soil samples and disruption of soil aggregates can increase C and N mineralization Richter et al. 1982 Gregorich et al. 1989 is indirect evidence of the existence of physical protection in soil. It has been concluded that there is more physical protection in fine-textured soils than in coarse-textured soils leading to higher carbon C contents and larger amounts of microbial biomass Jenkinson 1988 Amato and Ladd 1992 Hassink 1994 . Several mechanisms have been suggested to explain the physical protection of organic matter in soil against decomposition. Tisdall and Oades 1982 have mentioned the adsorption of organics on or coating by clay particles. Another explanation is the entrapment of organics in small pores in or between aggregates which renders them inaccessible to the decomposing microbial community Elliott and Coleman 1988 . Soil structure may also control decomposition processes by its effect on the grazing intensity of the soil fauna on microbes. The soil fauna may stimulate microbial growth rates through grazing Clarholm 1985 Coleman et al. 1978 and predation of microbes by protozoa and nematodes has been suggested as an important mechanism of nutrient turnover in soil Coleman et al. 1978 Elliott et al. 1980 . A large proportion of bacteria may occupy 1997 by CRC Press LLC pores 3 qm Kilbertus 1980 while protozoa and nematodes are restricted to larger pores. This .